luogu2870 [USACO07DEC]最佳牛线，黄金Best Cow Line, Gold

ref

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
int nn, n, rnk[60005], tmp[60005], cnt[60005], m=128, p, saa[60005];
char s[15], ss[60005];
void sasort(){
	for(int i=0; i<m; i++)	cnt[i] = 0;
	for(int i=0; i<n; i++)	cnt[rnk[i]]++;
	for(int i=1; i<m; i++)	cnt[i] += cnt[i-1];
	for(int i=n-1; i>=0; i--)	saa[--cnt[rnk[tmp[i]]]] = tmp[i];
}
void getSuffixArray(){
	for(int i=0; i<n; i++){
		rnk[i] = ss[i];
		tmp[i] = i;
	}
	sasort();
	for(int j=1; p<n; j<<=1){
		p = 0;
		for(int i=n-j; i<n; i++)	tmp[p++] = i;
		for(int i=0; i<n; i++)
			if(saa[i]>=j)
				tmp[p++] = saa[i] - j;
		sasort();
		p = 1;
		swap(rnk, tmp);
		rnk[saa[0]] = 0;
		for(int i=1; i<n; i++)
			if(tmp[saa[i-1]]==tmp[saa[i]] && tmp[saa[i-1]+j]==tmp[saa[i]+j])
				rnk[saa[i]] = p - 1;
			else
				rnk[saa[i]] = p++;
		m = p;
	}
}
int main(){
	cin>>nn;
	for(int i=0; i<nn; i++){
		scanf("%s", s);
		ss[i] = ss[2*nn-i] = s[0];
	}
	n = nn * 2 + 1;
	getSuffixArray();
	int A=0, B=nn+1;
	while(A+B-nn-1<nn){
		if(rnk[A]<rnk[B])	printf("%c", ss[A++]);
		else	printf("%c", ss[B++]);
		if((A+B-nn-1)%80==0)	printf("
");
	}
	return 0;
}